1. Field of the Invention
This invention is in the field of organic chemistry.
2. Description of the Prior Art
Cytokinins are a generic class of substances which promote cell division and growth and which occur at the purine, ribonucleoside and ribonucleotide levels in plants, as well as in the transfer RNA's of most forms of life. See Skoog, F. and Armstrong, D. J., Ann. Rev. Plant Physiol., 21, 359 (1970).
There are other classes of compounds which have more recently been synthesized which are structurally related to cytokinins, but act as cytokinin antagonists or anticytokinins in certain plant bioassays. It is postulated that such cytokinin antagonists could be employed to regulate plant development and the biosynthesis of specific products such as proteins, vitamins, chlorophyll and other compounds which the plant uses, for example, in energy metabolism and in adjustment to its environment. In addition, such cytokinin antagonists might be used to study plant cell genetics because they are an appropriate means to prevent mitosis or cytokinesis while manipulating cells to cause cell fusions or differentiation. These cytokinin antagonists can be used alone or in combination with cytokinins to interrupt, for short periods of time, the normal cytokinin effects on growth, etc.
It has also been disclosed that cytokinin antagonists can be used to achieve certain physiological effects in animal cells. For example, in U.S. patent application Ser. No. 740,287, filed Nov. 9, 1976, it is disclosed that cytokinin antagonists can be used to regulate intracellular levels of cyclic AMP. In U.S. patent application Ser. No. 674,003, filed Apr. 5, 1976, it is disclosed that one cytokinin antagonist, namely 3-methyl-7-n-pentylaminopyrazolo[4,3-d]pyrimidine, is a particularly potent regulator for human cells which are growing, such as PHA-transformed human lymphocyte cells.
Although there are several classes of compounds which have been described as possessing cytokinin antagonist activity, the class of 7-alkylamino-3-methylpyrazolo[4,3-d]pyrimidine compounds is still one of the more important. The cytokinin antagonist activity of this class is particularly described in U.S. patent application Ser. No. 285,677, filed Sept. 1, 1972 now abandoned.
Despite their increasing importance, it has previously been impossible to produce these compounds in high yields, reasonable amounts, and good purity because of the problems encountered with all known syntheses. For example, 3-methyl-7-n-pentylaminopyrazolo[4,3-d]pyrimidine was first synthesized by displacement of the S-methyl group of 3-methyl-7-methylthiopyrazolo[4,3-d]pyrimidine with n-pentylamine. See Skoog, F. et al, Phytochemistry, 72, 25 (1973). Although the desired antagonist could be obtained in fairly good yield from this reaction, it had to be purified on a chromatographic column. Additionally, some of the precursors to the 7-methylthio analogue were obtainable only in moderate yields, which lowered the overall yield for the complete synthesis to the order of only about 1%. In addition to this low overall yield, the resultant product had only fair purity. Additionally, and possibly more seriously, this synthetic scheme could only be carried out on a very small scale and did not lend itself to being scaled up to produce reasonable quantities of product.